EPI: Ends Per Inch (Threads per Inch): 
Unit for the density of the carcass fabric, measuring the number of nylon threads per square inch of casing material. The higher the EPI, the denser, more supple and lighter the casing is and thus the higher the quality of the tire. Lower EPI casing provides better puncture protection but makes for a stiffer and heavier tire.

The number stated here represents the EPI count for each individual layer in the three plies of casing. Other companies may give the total number of fabric threads of all layers in the casing construction.